The invention pertains to wireless detectors usable in alarm systems. More particularly, the invention pertains to such detectors which incorporate single die, multi-function, programmed processors configured for energy efficient battery powered operation.
Wireless ambient condition detectors are known. Such detectors, most conveniently, have been battery powered so that they may easily be mounted in a variety of locations without any need for power or communications cables. Known wireless detectors, while effective, have used energy at a rate which did not provide as long a battery life as desirable.
Known detectors have used separate integrated circuits to interface with different types of sensors such as smoke sensors and heat sensors. Signal processing has in turn required other circuits.
One type of circuit which has been used in detectors which incorporate smoke sensors have been application specific integrated circuits (ASIC). ASIC can be very inexpensive and cost effective in high volume, long run products. They are, however, expensive to develop, have long production lead times, and provide little or no flexibility. In addition, conventional ASIC contribute to higher than desirable power requirements.
Known detectors have used a different ASIC for communications and low battery detection. Since the ASIC coupled to the respective smoke sensor and the communications ASIC operate autonomously, they create irregular and unpredictable current draw profiles. In known detectors, this irregular and unpredictable current draw profile impedes accurate battery voltage measurements. As a result of these unpredictable current draws, low battery trouble, voltage thresholds have had to be set higher than desirable. This also contributes to shorter battery life.
Other known prior art detectors use an ASIC to couple electrical energy from the battery to an audible alarm indicating device in the detector. This produces a need for yet another, separate, circuit which must be interconnected with the rest of the circuitry of the detector and which contributes to further current draw.
Additionally, sensitivity compensation, to take into account dust and aging of a sensing chamber, has in some known systems been carried out at a system control panel. Smaller, less expensive control panels may not have the processing capability to implement this function.
One known type of detector based compensation provides a maximum incremental change which can take place in the detector during each compensation cycle. While this process does provide compensation over a period of time, the greater the extent of the required compensation, the longer is the time interval that is required to achieve a desired sensitivity.
Some known detectors which incorporate heat sensors have recognized that heat sensors can be susceptible to nuisance conditions such as electrical noise from static electricity, power surges, radio-frequency interference, as well as thermal noise both from turning the sensor on and off as well as thermal variations from the ambient environment. It has been known to use reference heat sensors to compensate for temperature changes. Such reference heat sensors not only add additional cost to the respective detector but are limited in the thermal noise which can be rejected.
It would be desirable therefore to provide highly energy efficient, multiple sensor detectors which require fewer integrated circuits. Preferably, such detectors could be implemented in a way so as to provide on-going flexibility to designers as product needs evolve, while at the same time extending battery life and providing enhanced rejection of nuisance signals.
A wireless detector incorporates a single chip, or die, integrated control element. The element includes an integrally formed processor, read-write, reprogrammable read only memory or one time programmable read only memory. Different memory types can be formed on the same die. The same chip can include programmable timers, and I/O ports for both analog and digital inputs or outputs.
In one aspect, the detector includes a photoelectric smoke sensor and at least one heat sensor. Executable instructions implement a common sensing cycle for both types of sensors. Two heat sensors can be incorporated into a disclosed embodiment.
In another aspect, a battery used to power the detector provides an output voltage in a predetermined monitorable range which will support successful operation. A voltage multiplier circuit, coupled to the battery, provides a higher voltage to drive an audible output device in accordance with processor supplied modulation.
In yet another aspect, the detector conserves energy, and extends battery life, by performing sensor sampling and signal processing functions for that sample interval during a single active interval. Then, the circuitry enters a low power, inactive state until the next activate interrupt arrives.
A disclosed embodiment combines different types of sensors, some of which have longer stabilization intervals then others. Different types of sensors can be activated simultaneously. Those with relatively short stabilization intervals can be sampled and the respective signal, or signals, processed, at least in part, during longer stabilization and processing intervals for other types of sensors. This overlap contributes to minimal over-all energy usage during each active interval.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.